Background:
The interscalene continuous peripheral nerve block (CPNB) is an effective regional anesthesia technique for prolonged analgesia after various painful shoulder and proximal arm surgeries. Secondary block failure, defined as failure of the block catheter to provide postoperative analgesia, is a frequent known complication.1 We hypothesize that injection of local anesthetic (LA) through the needle (TTN) prior to the insertion of a catheter can lead to undiagnosed improper catheter placement potentially resulting in a higher catheter failure rate compared to LA injected through the catheter only (TTC).
Methods:
Our Institutional Review Board approved this retrospective chart review study. All patients receiving an interscalene CPNB catheter at a single institution for postoperative analgesia and admitted for at least 24 hours were identified from July 2015 to June 30, 2016. We excluded patients on >30 mg morphine equivalents daily and those in whom injection technique could not be confirmed from charting. All blocks were performed by trainees (residents or fellows) supervised by an experienced regional anesthesia attending physician. Injection technique was determined by the procedure note charted in our electronic medical record. A secondary survey of the attending physicians was performed to confirm injection technique and practices. Primary outcome was visual analogue scale (VAS) pain scores at 7am on postoperative day 1, with secondary outcomes of opioid requirements in the postanesthesia care unit (PACU) and 24 hours after discharge from PACU. Data were analyzed for normality using the Shapiro-Wilk test and nonparametric data compared with the Mann-Whitney U test using R Studio open source software.
Results:
During the study period, 306 patients received an interscalene CPNB catheter and 205 met inclusion criteria. 24 patients had LA injected TTN and 181 injected TTC. Mean (SD) VAS at 7 am was 3.44 (2.78) TTC vs. 2.32 (2.41) TTN; p=0.0418. Opioid requirements (mg morphine equivalents) in the PACU was 17.2 (26.5) TTC vs. 31.33mg (34.82) TTN; p=0.0445. Opioid requirements at 24 hour was 64.4mg (68.64) TTC vs. 131.35mg (121.02) TTN; p=0.0003.
Conclusion:
Our study shows that patients in the TTC group reported better pain scores at 24 hours and required less opioid both in the PACU and at 24 hours compare to the TTN group suggesting better analgesia in the TTC group. Only 1 prior study has compared the 2 injection modalities but only to assess the effect on primary failure and not on secondary failure.2 Our study is limited by its retrospective nature. It is also possible that the difference is linked to other factors such as technical variations within each supervising attendings’ practice.
References
1) Ahsan ZS, el al. J Hand Surg Am. 2014 Feb;39(2):3249.
2) Slater ME, et al. Reg Anesth Pain Med. 2007 JulAug;32(4):296302.
